The distinction between zero-sum games (ZSG) and nonzero-sum games (NZSG) is not trivial. A player playing a ZSG cannot gain if prohibited to use certain strategies. This is not the case in NZSGs. In ZSG, the player does not benefit from exposing his strategy to his rival and is never harmed by having foreknowledge of his rival's strategy. Not so in NZSGs: at times, a player stands to gain by revealing his plans to the "enemy". A player can actually be harmed by NOT declaring his strategy or by gaining acquaintance with the enemy's stratagems. The very ability to communicate, the level of communication and the order of communication - are important in cooperative cases. A Nash solution: 1. Is not dependent upon any utility function; 2. It is impossible for two players to improve the Nash solution (=their position) simultaneously (=the Paretto optimality); 3. Is not influenced by the introduction of irrelevant (not very gainful) alternatives; and 4. Is symmetric (reversing the roles of the players does not affect the solution). The limitations of this approach are immediately evident. It is definitely not geared to cope well with more complex, multi-player, semi-cooperative (semi-competitive), imperfect information situations. Von Neumann proved that there is a solution for every ZSG with 2 players, though it might require the implementation of mixed strategies (strategies with probabilities attached to every move and outcome). Together with the economist Morgenstern, he developed an approach to coalitions (cooperative efforts of one or more players - a coalition of one player is possible). Every coalition has a value - a minimal amount that the coalition can secure using solely its own efforts and resources. The function describing this value is super- additive (the value of a coalition which is comprised of two sub-coalitions equals, at least, the sum of the values of the two sub-coalitions). Coalitions can be epiphenomenal: their value can be higher than the combined values of their constituents. The amounts paid to the players equal the value of the coalition and each player stands to get an amount no smaller than any amount that he would have made on his own. A set of payments to the players, describing the division of the coalition's value amongst them, is the "imputation", a single outcome of a strategy. A strategy is, therefore, dominant, if: (1) each player is getting more under the strategy than under any other strategy and (2) the players in the coalition receive a total payment that does not exceed the value of the coalition. Rational players are likely to prefer the dominant strategy and to enforce it. Thus, the solution to an n-players game is a set of imputations. No single imputation in the solution must be dominant (=better). They should all lead to equally desirable results. On the other hand, all the imputations outside the solution should be dominated. Some games are without solution (Lucas, 1967).